I am not 100% sure but I would tend to believe that the OnStar signal might be compromised with that style fin on your SRX. It looks like that nice looking fin is designed for AM & FM only. It doesn't say if it is compatible with OnStar as far as I can read. It looks as if it is designed to replace short style antennas only.Here's what I installed on my SRX. Very happy with it.
In researching this issue as it relates to my pending purchase of an SRX after the first of the year I came across this. Prior model years may be different.The OnStar coil is in the antenna base, only AM/FM use the arial portion.